TO_CHAR with dates to get week number issue

Question

I am trying to build a report showing weekly sales data and running into an issue with Dates and TO_CHAR..
Using the date 9/29/2007, I expect the return from the following to be 4:
SELECT TO_CHAR('09/29/2007','W') FROM DUAL
However, it returns 5!!! Testing further I tried the next day, since it is a Sunday, it should be the start of the next week, 5..
SELECT TO_CHAR('09/30/2007','W') FROM DUAL.. I do get a 5..
I understand that the implementation of TO_CHAR with the 'W' parameter defaults a week start on what ever the first day of the month is, but I need a method that is more calendar like (Sunday is the start of a week, Saturday end of the week).
Anyone have a nifty solution?
Thank you,
Tony Miller
UTMB/EHN

Answer 1

This works pretty well. Please note that it is zero based, so add 1 if you want it to start with the first week as 1.
WITH TAB AS
  (SELECT TO_DATE('12/01/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/02/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/03/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/04/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/05/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/06/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/07/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/08/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/09/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/29/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/30/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL UNION ALL
   SELECT TO_DATE('12/31/2007', 'mm/dd/yyyy') DATE_COL FROM DUAL)
SELECT DATE_COL,
  TO_CHAR(DATE_COL, 'ww') W_IN_YEAR,
  TO_CHAR(TRUNC(DATE_COL, 'month'), 'ww') W1_OF_MONTH,
  TO_NUMBER(TO_CHAR(DATE_COL, 'ww')) -
  TO_NUMBER(TO_CHAR(TRUNC(DATE_COL, 'month'), 'ww')) MY_WEEK,
  TO_CHAR(DATE_COL, 'W') ORACLE_WEEK
FROM TAB
DATE_COL     W_IN_YEAR W1_OF_MONTH MY_WEEK  ORACLE_WEEK
01-DEC-2007  48        48          0        1          
02-DEC-2007  48        48          0        1          
03-DEC-2007  49        48          1        1          
04-DEC-2007  49        48          1        1          
05-DEC-2007  49        48          1        1          
06-DEC-2007  49        48          1        1          
07-DEC-2007  49        48          1        1          
08-DEC-2007  49        48          1        2          
09-DEC-2007  49        48          1        2          
29-DEC-2007  52        48          4        5          
30-DEC-2007  52        48          4        5          
31-DEC-2007  53        48          5        5          
12 rows selected